In his six years as an Army recruiter in South Dakota and now in Chicago, Sgt. 1st Class Roger White has heard his pitch rejected for all kinds of reasons: The job is too dangerous. My parents hate the war. I can make more money working.

But when White tried to explain why he trusted that the military could continue to sustain and swell its ranks at a time of war, he said, one story came to mind.

A 39-year-old woman who once worked as a chemical specialist in the Army found herself down and out and living in a women’s shelter, he said. The Army came calling one more time, and she re-enlisted. Now, the woman is back in uniform at her previous job, serving in South Korea.

“It was amazing to see how much change we could bring to just this one woman’s life,” White said.

More recruits may soon be needed. With President Bush’s declaration last week that he had asked Robert M. Gates, the new defense secretary, to work with the Joint Chiefs of Staff on a plan to expand the Army and Marine Corps, military officials have already begun to consider how to grow, by how much and how fast.

Senior Army officials underscore the challenges they face, regardless of the goals that might be set. But like White, they also express confidence that the Army’s recruiters – armed with incentives, technology and inspiring stories from soldiers – can continue a steady, substantial annual increase in troop numbers.

The process is expected to be gradual: Pentagon civilian officials and military officers said that few are envisioning a large, rapid growth that would require the Army to dust off emergency mobilization plans for reopening bases or drawing in National Guard equipment.

Instead, civilian and military officials said, they are drawing up tentative proposals that would make permanent the 30,000-troop temporary increase approved by Congress after the terrorist attacks of Sept. 11, 2001, and then add 30,000 more troops to the Army over the next five years, resulting in an active-duty Army with 542,400 soldiers by 2012.

Expanding the nation’s ground forces is expensive; every 10,000 new soldiers add about $1.2 billion in personnel costs to the Pentagon’s annual budget. Equipment for 10,000 new troops would cost an additional $2 billion, according to Army statistics.

The study of how to expand the ground forces comes at a time of other financial strains. Army officials have told Congress that the service was $56 billion short in its equipment budget before the war in Iraq, and now requires an extra $14 billion annually just to repair and replace equipment worn or destroyed in Iraq and Afghanistan.

Nevertheless, among many officers and soldiers in Iraq and at home, the need for additional support has grown urgent. Gen. Peter J. Schoomaker, the Army chief of staff, previewed the service’s thinking this month when he warned that unless more soldiers were added to the roster, “We will break the active component.”

Schoomaker said the Army could successfully manage a growth of 6,000 to 7,000 soldiers a year, and a range of Army officials acknowledged that any growth larger or faster than that would require exorbitant amounts of money for financial incentives, new barracks and equipment.

Similarly, Gen. James T. Conway, the commandant of the Marine Corps, said recently that his force of 180,000 could grow by 1,000 to 2,000 a year until the current strain on America’s ground forces from the missions in Iraq and Afghanistan was reduced.

Col. Kevin A. Shwedo, director of operations for the Army Accessions Command, which is responsible for recruiting and initial training, said the service routinely reassigned drill sergeants and opened classrooms to fill specific Army needs, whether into field medicine, intelligence or infantry. This experience would allow the Army to deal with any order to expand its roster, he said.

“We have a plan right now where we have projected training seats from now through the end of next year,” Shwedo said in a telephone interview. “And we have the ability with minimal disruption to shift those seats if a decision is made by our military and civilian leadership to expand the training base.”

Recruiters still face challenges in filling basic training classrooms with new soldiers. The Army failed to meet its annual recruiting goals in 2005 by the widest margin in two decades.

The Army met its recruiting goal in the 2006 year, which ended at midnight on Sept. 30. But to be successful, the Army added 1,000 recruiters, bringing its total to 6,500, and sweetened educational and financial incentives.

The Army also raised recruits’ maximum allowable age to 42 from 35 and accepted a larger percentage of applicants who scored at the lowest acceptable range on a standardized aptitude examination, leading some military analysts to suggest that the Army had undermined its historic emphasis on quality to make its quota.

Sgt. 1st Class Abid Shah, a senior enlisted official at the military entrance processing station at Fort Hamilton in Brooklyn, N.Y., where new recruits are tested and sworn in, said more recruiters might be needed. Even then, he emphasized that the effort would move slowly.

“It won’t happen in days,” Shah said. “It takes years.”

Part of the struggle, recruiters said, is economic. Attracting young people to military service is difficult when jobs are plentiful and wages are on the rise.

The pool of eligible candidates is also small, as Army requirements that recruits meet certain physical, mental and moral standards mean that only three of 10 18-year-old Americans may apply.

Pentagon studies have shown that parents have increasingly become obstacles to recruitment. For some recruits, signing up means risking alienating parents, or just plain ignoring them.

Luis Vega, for example, after being sworn in to the Army Reserve on Friday at Fort Hamilton, said he had not told his parents.

“They think it’s just a phase,” he said.

His head was already shaved; he planned to ship out in April. And besides his fiancee, who he said supported the move, Vega, 28, said he was the only one in his hometown of East Rutherford, N.J., who seemed to understand the value of military service.

“Everybody thinks I’m crazy,” Vega said.

Elsewhere, especially in the Southwest, where recruiting has historically been strong, the mood seemed to be more visibly upbeat.

In Austin, Texas, Sgt. 1st Class Jeremy Cousineau said that there seemed to be no lack of interest among young men and women in his area.

Cousineau said he believed that the Army would have little trouble finding the soldiers it needed.

“It’s all good around here,” he said. “Life is good in recruiting for us.”